Diesel heaters and suppy voltage

[boatone]

Diesel heaters and supply voltage

I know I,m not the only one that has problems with this. Why are they so damned sensitive to supply voltage?
My Webasto refuses to start if the voltage is high just after a run and ditto if it drops below about 12.4
Previous Eberwotsit was just as bad.
Is it not possible to get a rectifier that provides stable supply from basic 12volt battery output?

 

[TrueBlue]

My Mikuni is almost as bad - starts and runs OK from 25-30V, but won't 24v. Mikuni say it should start at anything fro 22V. Fan, pump, etc is fine but electronics (?) just won't trigger the igniter.

Their techy says it's invariably a poor connection - go and scrape the connectors.

Now there's a blurry great hole in the engine bay, I might just well do that this weekend.

 

[RAI]

I had the reverrse probem with a Webasto, it would not start unless the alternator was holding the volts up above 13.6. The glow plug had to truely glow.

 

[oldgit]

I had the reverse probem with a Webasto, it would not start unless the alternator was holding the volts up above 13.6. The glow plug had to truely glow.

+1.
Eventually bit the bullet and rewired my heater.The original weedy wiring mysteriously wandered for miles round boat,voltage drop must have horrendus.
Heater never failed to fire when is was warm,only when it was cold and you desperately needed it to work.
Wired heater as directly as poss to batteries using monster thick cable.

 

[David2452]

It's not just about volts, volts are useless without current, a properly installed, serviced Webasto will start at 10.8v provided there is the capability to draw the current. Measure the voltage at the heater when its trying to start and see what it is. Almost invariably when I'm called to a problem such as you describe I find inadequate cables supplying the heater or dirty connections putting up resistance. Failing that a service usually cures it as the glowpin is so masked by carbon it needs more than the minimum current to get through it. One other problem I have come across is cheapskate Ebay ex vehicle units, some of which have a minimum voltage requirement of 11.6v instead of the usual marine requirement of 10.8v

 

[oldgit]

" One other problem I have come across is cheapskate Ebay ex vehicle units, some of which have a minimum voltage requirement of 11.6v instead of the usual marine requirement of 10.8v"

Curious that have never ever seen this mentioned in any material issued by any of the manufacturers,would that be purely for a large fleet supply or for say the heaters fitted to the Chrysler Voyager of which doubt more than one or two would come with this option fitted.?
Can say for a fact that when you start up a "well used" version with a diesel the drop is well below 11 volts.

 

[David2452]

Nothing curious about it, there is no reason for you to have seen it published, most of the PDF manuals and other stuff on the net cover only the basics for DIY and not in depth information. Just as an example the Webasto AT3500ST fitted to VW vehicles has vehicle battery protection to allow it to shut down or not start below 11.6v, furthermore it will not run without W bus input from the vehicle it is normally fitted to and only puts out 3kw max instead of the usual 3.5kw, there are many examples of similar peculiarities not obvious to an untrained eye simply looking at the heater. But even aftermarket non W bus controlled Webasto vehicle heaters have a different ECU and in some cases a different fan motor to a Marine / Motor Caravan unit, still work in a boat but not as well when hooked up to long ducts.
Absolutely can say that they start at the specified minimum voltage of for example 10.8v when properly serviced, when I do the after service test and reports part of the procedure is to run heaters from an adjustable voltage bench supply and reduce to minimum and increase to maximum spec to ensure heaters I have serviced have been returned to spec. If by well used you mean neglected and not serviced then voltage drop can be an issue even with decent weight clean and bright cabling. Most good installs that show a healthy voltage at the ECU and no other faults when I plug my diagnostic kit to them and will not start simply need a decoke service service.
My test kit measures voltage drop at the ECU which is the important place and I often see well below 11v on neglected or poorly executed installations, terminal, rubbish fuse contact cleaning or cable uprating usually cures it at a stroke

 

[oldgit]

Thanks for explaining that,rather interesting.

 

[boatone]

Well, the engineer came today and did a thorough job of assessing the wiring and voltage drops etc and decided that the main cable loom between the Webasto and the battery was suspect - looked as if current heater was a later fit but used old Eberspacher wiring.
Net result was an improvement of about 1 volt as sensed at the heater so a distinct improvement. Now starts first time so remains to be seen how it behaves if faced with partly discharged batteries.
I hadn't appreciated that the switch circuit simply sends an on off to the heater itself which then draws its operating current over a separate loom directly from the batteries.
Fingers crossed !

Thought you might like to see what a voltage log looks like after a 4 day cruise :

(PS - a warm day probably not the best time to have 2Kw of heating running in the cabin )

 

[CX54WEK]

Our Webasto (2000ST) canT be that fussy then. Starts anywhere from 13.7V right down to 11V.

(And yes I know batteries shouldnt be let down to 11V )

 

[boatone]

Our Webasto (2000ST) canT be that fussy then. Starts anywhere from 13.7V right down to 11V.
(And yes I know batteries shouldnt be let down to 11V )

Working range should be 10.5 volts to 15 volts but that is the voltage seen by the heater itself, not at the battery, so poor cabling losses can be an issue as we think was the case with mine (same model as yours).
Now I need to get a handle on just how much power the bl**dy fridge is consuming !

 

[prof pat pending]

Get a clamp meter...they can be bought quite cheaply from places like maplin, and you should be able to see exactly what each item is drawing as you switch them on and off

 

[maby]

Get a clamp meter...they can be bought quite cheaply from places like maplin, and you should be able to see exactly what each item is drawing as you switch them on and off

Will a clamp meter work on DC? never actually owned one myself, but I had the impression they were AC only.

 

[prof pat pending]

Most will measure voltage, some will measure current

It's worth checking that it does exactly what you want first

Foe example, this one does both
http://www.maplin.co.uk/dc-ac-current-clamp-multimeter-629713
Although the min amps may be a little high

 

[boatone]

Get a clamp meter...they can be bought quite cheaply from places like maplin, and you should be able to see exactly what each item is drawing as you switch them on and off

The display panel for my Adverc battery management system lets me see everything - volts at battery post, amps charge or discharge for both engine and domestic batteries. Also I can monitor voltage at positive terminals of the alternators - probably too much information for my own good !

I can see exactly how much current is taken by anything I switch on but have yet to do a test over a few hours to verify actually fridge drain - watch this space as I have good reason to believe its lot more than the 3.7 amps it says on the fridge plate !